1. Field of the Invention
The present invention relates generally to transmitters, and particularly, to such a transmitter that operates in accordance with a frequency plan to reduce spurious energy in the transmitter.
2. Related Art
A conventional communication transceiver includes a transmitter to generate an output signal having a tunable output signal frequency. One type of known transmitter is a translational-loop transmitter. The translational-loop transmitter includes an offset phase-locked-loop (PLL) to generate the output signal and phase-lock the output signal to a reference signal. The offset PLL includes an offset mixer in a feedback path of the PLL.
Devices used in the offset PLL, particularly the offset mixer, may have non-linear device characteristics tending to give rise to undesired spurious energy, known as “spurs,” in the PLL. Often, the spurs are generated at frequencies and power levels that interfere with, and thus degrade, transmitter performance. One approach for minimizing the spurs is to use highly linear devices in the PLL, such as a highly-linear offset mixer. However, such highly linear devices are generally expensive. Therefore, there is a need to minimize or avoid spurs in a translational-loop transmitter, without resorting to such expensive, highly linear devices.
The competitive mobile communication market demands a compact, low cost, and low power transmitter for use in a communication transceiver. It is also desirable that the transmitter be capable of generating an output signal at a frequency in any one of multiple frequency bands, including the Global System for Mobile Communications (GSM), Digital Cellular Service (DCS), Personal Communication Service (PCS), and additional communication frequency bands, for example. Such transmitter operation is referred to as multi-band operation.
Therefore, there is a need for a transmitter that meets all of the above-mentioned needs.